Targeting Valuable Chemical Commodities: Hydrazine‐mediated Diels‐Alder Aromatization of Biobased Furfurals

Abstract

A hydrazine-mediated approach towards renewable aromatics production via Diels-Alder aromatization of readily available, biobased furfurals was explored as alterative to the more classical approaches that rely on reactive but uneconomical reduced dienes (e. g., 2,5-dimethylfuran). To enable cycloaddition chemistry with these otherwise unreactive formyl furans, substrate activation by N,N-dimethyl hydrazone formation was investigated. The choice of the reaction partner was key to the success of the transformation, and in this respect acrylic acid showed the most promising results in the synthesis of aromatics. This strategy allowed for selectivities up to 60 % for a complex transformation consisting of Diels-Alder cycloaddition, oxabridge opening, decarboxylation, and dehydration. Exploration of the furfural scope yielded generic structure-reactivitystability relationships. The proposed methodology enabled the redox-efficient, operationally simple, and mild synthesis of renewable (p-disubstituted) aromatics of commercial importance under remarkably mild conditions.

Insights into Endo/Exo Stereopreference in Diels–Alder Cycloadditions of Chitin-Derived Furans

“…Functional groups flanking the diene can significantly influence the rate and selectivity of DA cycloadditions. 35 Hence, chitinderived furans with different substituents at the 2-position were used to study differences in reactivity and the effects on endo/ exo selectivity (Table 3). D 2 O was selected as the initial solvent for alcohols (HEFA, HMFA, and Di-HAF) to avoid signal overlap in the NMR spectrum, hindering accurate quantification.…”

Tandem Isomerization/α,β-Site-Selective and Enantioselective Addition Reactions of N-(3-Butynoyl)-3,5-dimethylpyrazole Induced by Chiral π–Cu(II) Catalysts

“…Furans have recently received particular attention in [4 + 2] cycloaddition reactions, as they are crucial renewable-platform molecules with great potential for the more sustainable production of chemical building blocks and materials. 17 In contrast, the reaction of 2 with acyclic dienes gave no desired cycloadducts probably due to the instability of 2 and low reactivity of acyclic dienes.…”

On the Valorisation of Chitin-Derived Furans by Ball Milling.

“…In some cases, DA reactivity is enabled by chemical derivatisation of electron-poor furans, with reduction, hydration or hydrazone formation reactions. [25,[37][38][39] Regarding to this, formyl derivatisation with a hydrazine auxiliary stands out as powerful strategy due to significant increase in the orbital coefficient at the C-5 position, because the delocalization of nitrogen electron pairs in the hydrazone substituent by resonance effect (Scheme 1b). [38][39][40][41][42] After DA reaction, it leads to the aromatisation reaction spontaneously, even at temperatures lower than 50 °C.…”

“…[25,[37][38][39] Regarding to this, formyl derivatisation with a hydrazine auxiliary stands out as powerful strategy due to significant increase in the orbital coefficient at the C-5 position, because the delocalization of nitrogen electron pairs in the hydrazone substituent by resonance effect (Scheme 1b). [38][39][40][41][42] After DA reaction, it leads to the aromatisation reaction spontaneously, even at temperatures lower than 50 °C. Although the usual approach has provided the formation of aromatic compounds with high-added value, the reactions are limited by the use of N,N-dimethylhydrazine and more recently 1-aminopyrrolidine (Scheme 1c).…”